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What is RPF?
RPF is a rare fibroinflammatory retroperitoneal process that most commonly occurs in the fifth to sixth decades of life. Two thirds of cases are idiopathic in nature (in which case it is also known as Ormond’s disease), and one third of cases develop in response to ergot derivatives and other medications or retroperitoneal metastatic disease (in which case it is called malignant RPF). Up to 15% of cases occur in association with other fibroinflammatory processes such as fibrosing mediastinitis, orbital pseudotumor, primary sclerosing cholangitis, and Reidel’s thyroiditis. RPF typically arises in the inferior retroperitoneum at the lumbosacral level and may extend superiorly to the renal hila, sometimes encasing and obstructing one or both ureters.
What are the CT and MR imaging features of Retroperitoneal fibrosis?
Homogeneous soft tissue is typically seen in the retroperitoneum in a periaortic and pericaval distribution, sometimes with hydroureteronephrosis due to ureteral encasement. It has intermediate-slightly high attenuation, low-intermediate signal intensity on T1-weighted images, either low signal intensity (when mature and benign) or high signal intensity (when immature or malignant) on T2-weighted images relative to skeletal muscle, and variable enhancement. Benign RPF typically does not cause anterior aortic displacement or lateral ureteral displacement. Malignant RPF is more likely to be present when lymphadenopathy or metastatic disease elsewhere in the body, an ill-defined heterogeneous mass, or adjacent osseous destruction is observed.
